Relay and relay system



y 1936- w. J. HUDSON 2,046,748

RELAY AND RELAY SYSTEM Filed Feb. 19, 1932 4 Sheets-sheet 1 F .3 I 52 f] 49 .1: u h llj Y WITNESSES: 50 59 INVENTOR 2% v Y Wz'ZZz'am JHUdSO/T. in mwwxw. B

July 7,1936. I w, HUD N 2,046,748

RELAY AND RELAY SYSTEM Filed Feb. 19, 1932 4 Sheets-Sheet 2 2 WITNESS s: INVENTOR ATTORNEY I July 7, 1936. w, J, HUDSON 2,046,748

RELAY AND RELAY SYSTEM Filed Feb. 19, 1932 4 Sheets-Sheet 3 I III vats?" WINESES: INVENTOR I M/zZ/z'am JHz/dson.

Patented July 7, 1936 UNITED STATES RELAY AND RELAY SYSTEM William J. Hudson, Wilkinsburg, Pa., assignor to Westinghouse Electric & Manufacturing Company, a corporation of Pennsylvania Application February 19, 1932, Serial No. 594,009

12 Claims.

My invention relates generally to relays and more particularly to alternating-current relays.

An object of my invention is the provision of an alternating-current relay that shall be simple and reliable in operation and economically manufactured and installed.

Another object of my invention is to provide a substantially definite time delay action in the operation of an alternating-current relay.

A further object of my invention is to provide for establishing a unidirectional flux in the magnetic circuit of an alternating-current relay and for gradually and positively dissipating said flux to insure the positive functioning of saidrelay a predetermined length of time after the relay is deenergized.

A still further object of my invention is to provide a unidirectional flux in the magnetic circuit of an alternating-current relay in order to prevent the armature of the relay from vibrating or chattering as the alternating current passes through zero.

It is also an object of my invention to provide for establishing a limited amount of unidirectional flux in the magnetic circuit of an alternating-current relay so that the impedance of the alternating current Winding of the relay remains substantially unchanged.

Another object of my invention is to provide for operating a plurality of alternating-current relays in timed sequence, the interval between each successive operation being effected by the time delay action inherent in each relay.

A still further object is the provision of an alr temating-current relay that will operate on a relatively low frequency and at the same time prevent chattering and vibrating of its armature.

Other objects of the invention will hereinafter become apparent. For a fuller understanding of the nature and the objects of my invention, reference should be had to the following detailed description, taken in connection with the accompanying drawings, in which:

Figure 1 is a partially diagrammatic and a partially side elevational view of a relay embodying the features of my invention;

Fig. 2 is a partially diagrammatic and a partially side elevational view of a modified form of a relay embodying the features of my invention;

Fig. 3 is a top plan view of the relay shown in Fig. 2;

Fig. 4 is a diagrammatic view of a control system utilizing relays that are constructed substantially in accordance with the relay shown in Fig. 1; and

Figs. 5 and 6, respectively, show diagrammatic views of a control system utilizing relays that are constructed substantially in accordance'with the relay shown in Figs. 2 and 3, except that in Fig. 5 each relay is associated with a pilot relay and a mechanical interlock.

First, I will describe the construction and the operation of the relay shown in Fig. 1 followed by the accompanying control circuit in Fig; 4 which utilizes a plurality of such relays and, second, I will describe the construction and the operation of the relay shown in Figs. 2 and 3 followed by the accompanying control circuits shown in Figs. 5 and 6 which utilize a plurality of such relays.

Referring to Fig. 1, I have shown the constructional features of the relay partially diagrammatically, since my invention may be utilized in relays of any general construction.

Generally, the relay comprises a suitably mounted core 9 having a central-leg II and two end-legs l3 and M, an armature 12 disposed in vertical alignment with said legs, a main alternating-current winding l5 mounted upon the central-leg I l, a demagnetizing winding I1, and a winding l8, having an asymmetric unit IS in series therewith, mounted upon the leg H.

The core 9 may be mounted upon any suitable upright in in any well known manner such as by the illustrated bolts. In order to prevent saturation of the central leg ll, its cross sectional area is approximately twice the cross sectional area of each of the legs l3 and I4.

For the purpose of convenience, the flux path through the central-leg II and the upper end-leg I3 will hereinafter be referred to as the upper magnetic circuit and, similarly, the flux path through the central leg II and the lower-leg M will be referred to as the lower magnetic circuit.

As illustrated, the upper-leg I3 is somewhat shorter in length than the central-leg l l and the lower-leg 14, in order to provide an air gap H5 in the upper magnetic circuit.

The armature l2 may be pivotally mounted in vertical alignment with the ends of the legs 9 I, I3 and It in any suitable manner. As shown, a support 25, suitably mounted on the upright ill by means of the illustrated bolt, extends horizontally outward to provide a means for pivotally mounting the armature I2. A plate 40, having a tongue 24 that is integrally formed therewith and disposed upwardly at an angle of about 45, is mounted on the end of the support 25 and its straight bifurcated portion extends somewhat beyond the end of the support 25 in order to provide a notch in which the upper inside edge 30 of the armature l2 may be pivotally disposed. Attached at the upper end of the armature l2 and disposed substantially in parallel alignment with the tongue 24 is an ear 23.

As illustrated, the upper ends of the tongue 24 and the ear 23 are provided with an opening for the bolt 22. A coil-spring 20 encompasses the bolt 22 and is disposed between the ear 23 and from moving sideways.

For a more detailed description of a relay having such an armature mounting and a demagnetizing winding, reference may be had to Patent No. 1,753,983, issued to Willard G. Cook, April 8, 1930, and assigned to the assignee of this invention.

The armature is shown provided with two pairs of contacts but it is apparent that the armature may actuate any desired number of contacts. In order that the relay may be utilized in the control circuit shown in Fig. 4, I illustrate a set of contacts 32 and 33, bridged by the bridging member 36, and a contact 38 carried by the lower end of the armature and disposed to engage a contact 43 mounted on the end of the bolt 39. The contacts 32 and 33 are respectively carried by L-shaped arms 4i and 42 that are mounted on the upright Ill by means of bolts 34 and 35. The bridging member 36 is pivotally mounted on the armature i2 and is insulated therefrom by means of the pivotally mounted member 48, so that the circuits connected therethrough may be insulated from the contact member 38.

The main alternating current winding N5 of the relay is disposed to be connected across any suitable alternating-current source. In the operation of the relay, the fiux produced by the main winding IS, in the absence of the winding 98 and the asymmetric unit l9, would divide and circulate through the upper and the lower magnetic circuits in the inverse proportion to the reluctance encountered. Since the upper magnetic circuit is provided with an air gap iii, the greater portion of the flux produced by the winding 55, in the absence of the winding 18 and the asymmetric unit to, would circulate through the lower magnetic circuit.

The winding i8 and its associated asymmetric unit i9 provides for establishing a unidirectional flux, the greater portion flowing through the lower magnetic circuit and indicated by the broken line 44, which must be dissipated or decreased to a predetermined value having an attractive force less than the biasing force of the spring 20, before the armature I2 opens. In other words, the time delay action of the relay depends upon the time required to dissipate the unidirectional fiux to a predetermined value.

The asymmetric unit 59 may be of any wellknown type so long as it affords a relatively high resistance to the fiow of the current induced in the winding H3 in one direction and affords substantially no resistance to the flow of said current in the opposite direction.

Assume now that the fiux produced by the main winding i5 during the first quarter-cycle traverses the central-leg i I from left to right and, as explained hereinbefore, that the greater portion of the flux traverses the lower magnetic circuit. As the flux cuts the winding I8, a current would be induced in the windings were it not for the fact that the direction of its flow is such that the unit l9 prevents it from passing. In other words, during the first quarter-cycle, the winding I8 is in effect open-circuited by the unit l9. Consequently, the flux that is produced by the main winding I5 is permitted to traverse freely the lower magnetic circuit without being opposed by a flux set-up by the winding 18.

In the second quarter-cycle, the main iiux that is established during the first quarter-cycle, hereinafter referred to as the first quarter-cycle main flux tends to decay in the usual manner, but in doing so, it induces a current in the wind ing l8 of such direction that the unit l9 permits the induced current to fiow through it. Accordingly, the induced current establishes a flux of such direction as to oppose the decay of the said first quarter-cycle main fiux in the lower magnetic circuit. In this connection, it will be observed that since the winding l8 and the asymmetric unit l9 offer a slight resistance to the flow of the induced current, the decay of the said first quarter-cycle main flux will not be totally opposed by the flux established by the induced current, but will decay very gradually.

In the third quarter-cycle, the direction of the main flux, established by the winding l5, traverses the central-leg from right to left andit will be noted that this third quartercycle main flux which flows in the lower magnetic circuit induces a current in the winding l8 in addition to the induced current already established by the decaying action of the said first quarter-cycle main fiux. The flux produced by the circulating induced current present in the winding l8 during the third quarter-cycle, opposes the passage of the said third quarter-cycle main fiux in the lower magnetic circuit, with the result that the greater part of the said third quarter-cycle main fiux traverses the upper magnetic circuit, notwithstanding the air gap i6. It will be noted that, during the third quarter-cycle the rate of decay of the said first quarter-cycle main flux established in the lower magnetic circuit, is slightly faster than it was during the second quartercycle, since the said third quarter-cycle main flux is not totally opposed by the flux produced by the induced current of the winding Hi. In other words, that part of the said third quarter-cycle main flux which is not opposed during the third quarter-cycle, since it is opposite in direction, slightly reduces the said first quarter-cycle main fiux, in addition to the fiux decay action of the said first quarter-cycle main flux which is present during the third quarter-cycle, the same as it was during the second quarter-cycle.

In the fourth quarter-cycle, that small part of the said third quarter-cycle main fiux that was produced in the lower magnetic circuit decays, but

in doing so, no current is induced in the winding l8 since the asymmetric unit !9 prevents it. Therefore, the only action present in the lower magnetic circuit during the fourth quarter-cycle is the decay action of the said first quarter-cycle main flux. This rate of decay is substantially the same as it was during the second quarter-cycle.

From the foregoing, it will be noted that at the end of the fourth quarter-cycle, the said first quarter-cycle main fiux is of a certain quantity, that is, the action of the winding l8 and the asymmetric unit l9 prevents the said first quartercycle main flux in the lower magnetic circuit from decreasing to zero, but sustaining it at a certain value. The flux action in the remaining cycles of the main alternating-current flux is the same as that for the first cycle, except that the first quarter-cycle main flux of each successive cycle is cumulative or additive and, in consequence, the stored or unidirectional flux gradually increases until it substantially saturates the lower magnetic circuit.

However, as the unidirectional flux gradually builds-up to almost saturation point of the lower magnetic circuit, the main flux produced by the winding I5 tends to flow through the upper magnetic circuit, notwithstanding the air gap I6, because the stored or unidirectional flux of the lower magnetic circuit increases the reluctance thereof. In this manner, after the lower magnetic circuit becomes substantially saturated, the greater portion of the main flux traverses the upper magnetic circuit, with the result that the impedance of the main winding I5 is substantially unchanged so that the relay will operate in shunt or across a suitable supply of alternating current. In other words, the upper magnetic circuit constitutes a flux by-pass when'the lower magnetic circuit becomes substantially saturated with unidirectional flux, so that the impedance of the main winding is substantially unchanged.

In this connection, it will be noted that the unidirectional'flux provides for continuously attracting the armature to the core, with the result that it eliminates any vibrating or chattering of the armature.

When the main winding I5 is deenergized, the main alternating-current flux produced thereby immediately decays but the unidirectional flux continues to exist, decaying at a slow and gradual rate. When the unidirectional flux decays to a value having an attractive force less than the biasing force of the spring 20, the armature I2 of the relay opens. The time required in dissipating the unidirectional flux to such drop-away value affords a time-delay action in the operation of the relay.

In order to insure that the unidirectional flux will decay to a value having an attractive force less than the biasing force of the spring 20, the demagnetizing winding I1 is energized with a unidirectional current which establishes aflux that opposes or dissipates the residual magnetism of the unidirectional flux. In this manner, the unidirectional flux is positively dissipated and, in consequence, the operation of the relay is positive. The size of the conductor and the number of turns provided in the winding I'I depends upon the amount of unidirectional flux stored in the lower magnetic circu t and the time in which it is desired to dissipate the residual magnetism of the unidirectional flux. Usually the amount of current required for the winding I1 is very small and preferably, in most installations, since direct current is not generally available, the winding Il may be energized by unidirectional current provided by an asymmetric unit. Such an arrangement is shown in the accompanying control circuit in Fig. 4.

In this connection, it is to be understood that I do not intend to limit the application of the relay, shown in Fig. 1, to such a control circuit as shown in Fig. 4, but that I have simply illustrated one of its uses for the purpose of showing its general utility.

The control system in Fig. 4 comprises, generally, a motor 13 having a primary winding 14 and a secondary winding 15, a plurality of sets of accelerating resistors l6, l1 and 18, a main line switch 92 actuated by a relay 90, a plurality of relays 98, 99 and I00 constructed substantially in accordance with the relay shown in Fig. 1 and a drum controller 19 having a plurality of contact fingers IN to I01, inclusive, disposed to control the operations of the motor 13.

The motor 13 may be of any well-known type suitable for operation from a supply of threephase alternating current represented by the line conductors I0, 'II and I2. The secondary circuit 15 of the motor I3 is connected with a plurality of sets of accelerating resistors 10, TI and 16 which are disposed to be excluded in timed sequence by the operation of the relays I00, 99 and 98, respectively.

The relay 90 is substantially the same as the relay shown in Fig. 1, except that its armature is connected to operate the main line switch 92, and that no demagnetizing winding is provided to dissipate the residual-magnetism of the unidirectional flux. However, in this relay, I provide for reducing the residual magnetism to a value, to have an attractive force less than the biasing force of the illustrated spring, by means of a shim or non-magnetic member 93. As shown, the shim 93 is disposed on the end of the lower leg of the core of the relay 90 so that when the armature is closed an air gap is, in effect, provided. In consequence, the magnetic reluctance of the lower magnetic circuit is increased so that, when the relay is deenergized, the residual magnetism is decreased in substantially the same proportion as the reluctance of the lower magnetic circuit.

In this connection, it will be readily understood that if a demagnetizing winding, such as the winding I! in Fig. 1, were utilized to dissipate the residual magnetism of the relay 90, it would be of no utility upon a power failure, because there would be no current present to energize the demagnetizing winding.

However, in connection with'the demagnetizing windings of the relays 98, 99 and I00, I find that it is advantageous not to dissipate the residual magnetism, upon a power failure. Consequently, such of the relays as are closed, when the power failure occurs, remain closed since the attractive force of the residual magnetism is greater than the biasing force of the illustrated springs. When the power returns, provided the main switch 92 has not opened, the motor will continue to operate at the same speed as it did before the power failure.

The winding that surrounds the lower leg of the core of the relay and its associated asymmetric unit 89 are connected in circuit with the drum controller 19, so that when the controller is actuated to the off position, a, the circuit is open. By this arrangement, the instantaneous opening of the relay 90 may be effected on regular operations of the control system, that is by the operation of the drum controller 19. Otherwise, the operation of the relay 90 is substantially the same as that explained for the relay in Fig. 1.

Since the relay 90 affords a predetermined time delay before its armature opens after the main alternating current winding is deenergized it holds the main line switch 92 closed for a period of to 2 seconds upon a power failure of the main supply line. If the power returns before the relay 90 operates or opens the motor 13 continues to run, which avoids the necessity of restarting the motor with the drum controller 19, as would be the case if no time delay action were provided. For the purpose of insuring that the power, when it returns, will cause no injury to the motor 13, the time delay action of the relays 90, 98, 99 and I00 are so regulated by means of the illustrated coil springs and the adjustable nuts that the relay 90 opens the main line switch 92 before the relays 98, 99 and I00 open. Sup-- pose, for'example that the motor I3 is being operated below maximum speed, that is, with one or more sets ofthe accelerating resistors in the secondary'winding of the motor 13 and, if the time delay action of the relays 98, 99 and I90, is less than that of the relay 90, they will open to exclude all of accelerating resistors before the mainline switch 92 opens, and upon the return of the power the full voltage will be suddenly impressed on the motor, which is running at a low speed, with no resistance in the secondary winding of the motor 13. This condition may cause injury to the motor and at the same time causes the motor to run at maximum speed while the drum controller is set to give one or another of the slower speeds.

As illustrated, the neutralizing windings I22, I23 and I24 of the relays 98, 99 and I00 are energized by unidirectional-current supplied by the system of asymmetric units 80 energized by alternating current. The circuit for energizing the asymmetric units 80 extends from the line conductor 10 through conductor I25, the control switch I26, conductors I21 and I28, the asymmetric units 80, the resistor I44 and conductor I to the line conductor H. The demagnetizing winding for each relay is directly connected across the two unidirectional-current supply conductors I41 and I48. The demagnetizing winding I22 of the relay 98 is connected across the supply conductors I41 and I48 through conductors I62 and I63. Similarly, the demagnetizing winding I23 for the relay 99 is energized through conductors I64 and I66, and the demagnetizing winding I24 of the relay I00, through conductors I69 and I10. Consequently, the demagnetizing winding of each relay is continuously energized as long as the control switch I 26 is closed.

The closing of the control switch I26, in addition to energizing the demagnetizing windings, energizes the drum controller 19 and, in turn, the main windings of the relays 98, 99 and I00. The circuit for energizing the main winding of relay 98 extends from the energized drum controller 19 through the contact finger I05, conductors I3l and I32, the main winding of the relay 98, and conductors I33, I 34 and I35 to the line conductor 1I.

Similarly, the circuit for energizing the main winding of the relay 99 extends from the energized drum controller 19 through a contact finger I06, conductors I36 and I31, the main winding of the relay 99, conductors I38, I34 and I35 to the line conductor 1|. When the relay 99 closes an additional parallel circuit is established through the contacts 209 for energizing the main winding of the relay 98. This circuit may be traced from the energized conductor l21 through conductor 205, the contacts 206, conductors 201 and I32, the main winding of the relay 98, and conductors I33, I34 and I35 to the main line H.

The circuit for energizing the main winding of the relay I 00 extends from the energized drum controller 19 through a contact finger I01, conductor I39, the main Winding of the relay I00, and conductors I4I, I34 and I35 to the line conductor 1I. When the relay I00 closes, an additional parallel circuit is established through the contacts 202 for energizing the main winding of the relay 99. This circuit extends from the energized conductor I21 through conductor 203, the contacts 202, conductors 204 and I31, the main winding of the relay 99, and conductors I38, I34 and I35 to the main line conductor 1I. It will be noted that, as the relays I00, 99 and 98 close they, respectively, remove the shunts around the plurality of sets of resistors 18, 11 and 19 and thereby connect the said resistors in the secondary winding of the motor 13. the motor 13 is in condition for starting by closing the main line switch 92.

In the starting of the motor 13, the usual practice is to immediately actuate the drum controller to full on position, namely, position I and thereby let the acceleration be taken care of by the delayed action inherent in the relays I00, 99 and 96. Just as soon as the controller is actuated to position b, on its way to the full on" position, a circuit is established for energizing the main winding of the relay 90 which causes the said relay to close the main line switch 92.

The circuit for energizing the relay 90 extends from the energized drum controller 19 through a contact finger I02, conductors 99 and 98, the main winding of the relay 90, and conductors I34 and I35 to the main line conductor 1I. As soon as the relay 90 closes the main line switch 92, alternating current is supplied to the primary of the motor 13. Also, concurrently with the closing of the switch 92, a holding circuit is established by means of the contacts 94, for continuously energizing the relay 90 when the drum controller is advanced to positions, 0", d, e and f. The holding circuit may be traced from the energized drum controller 19 through a contact finger I04, conductor I1I, the contacts 94, conductor 98,

the main winding of the relay 90, and conductors I34 and I35 to the main line conductor 1|.

Therefore, when the drum controller 19 is advanced beyond the position b, the holding circuit, just described, is the only means for continuously energizing the relay 90. In this manner, a low-voltage protection is provided for the control'system because the relay 90 will operate to open the main line switch 92 when the voltage of the supply line falls below a predetermined value. That is to say, when the relay 90 opens, as a result of the low voltage condition, it will not pick-up when the power returns on the line conductors, unless the drum controller is actuated back to position b.

When the drum controller 19 is advanced to position d", as it is being actuated to the full on position I, the circuit that energizes the relay I00 is interrupted, then, after a predetermined length of time, depending on the time delay action afforded by the unidirectional flux, the relay I00 closes its contacts I85 to shunt out or exclude the set of resistors 19 from the secondary circuit of the motor 13. The shunting circuit comprises the conductors I82, I83 and I84 and the contacts I85 of the relay I00.

Simultaneously, with the operation of the relay I00, one branch of the parallel circuit that energizes the main windings of the relay 99 is interrupted through the opening of the contacts 202, while the other branch of said parallel circuit is interrupted at the contact finger I05, since I am assuming that the drum controller 19 is in position I. Accordingly, a predetermined length of time after the deenergization of the relay 99, the said relay closes its contacts I8I to shunt out or exclude the set of resistors 11 from the secondary circuit of the motor 13. The shunting circuit comprises the conductors I18, I19 and I80 and the contacts I8I of the relay 99.

The operation of the relay 99, interrupts one branch of the parallel circuit that energizes the main winding of the relay 98 through the opening of the contacts 206 while the other branch This means that of the said parallel circuit-is interrupted at the are connected contact finger l 04. After a predetermined length of time from the interruption of the circuit for the main winding of the relay 98, the said relay closes its contacts I 11 to shunt out or exclude the set of resistors 16 from the secondary of the motor 13. The shunt circuit comprises the conductors I14, I15 and I16 and the contacts II'l of the relay 98.

From the foregoing description, it is noted that the relays I00, 99 and 98 operate in time sequence to successively exclude the resistors 18, TI and 16 from the secondary winding of the motor circuit.

At this time I wish to point out that the time sequence operation of the relays may be efiected by a push-button instead of the controller contact 19, but by providing the drum controller 19, it is possible to obtain speed control of the motor as well as to provide for starting the said motor.

Whenever it is desirable to run the motor at a minimum speed, this may be accomplished by advancing the drum controller I9 to positions b or 0, preferably position 0, since it affords a low voltage protection for the control system. In either one of these positions the relays W6,

99 and 98 are energized, with the result that all of the sets of accelerating resistors 18, TI and 16 are included in the secondary circuit of the motor i3. However, if it becomes convenient to slightly increase the speed of the motor, this may be done by advancing the controller to position d. In this position the circuit for energizing the relay N10 is interrupted at contact finger I86 and the relay I80, after a predetermined length of time, operates to exclude the set of resistors 18 from the secondary winding of the motor l3.

In a similar manner, the speed may be further increased by advancing the controller to position e, which causes the relay 99 to exclude the sets of resistors i8 and i1 from the secondary winding of the motor 13. The maximum speed is finally attained when the controller is advanced to the full-on position f. In this position the relay 98 excludes all of the resistors from the secondary winding of the motor i3.

Therefore, the control circuit, shown in Fig. 4, illustrates a very useful application of the relay shown in Fig. 1, but it is to be understood that I do not intend to limit the utility of my relay to such a control system, since my relay has universal application.

Referring now to Figs. 2 and 3 of the drawings, I will describe a modified form of my relay which finds useful application in the control circuit illustrated in Figs. 5 and 6. In Figs. 2 and 3, I have illustrated the modified form of my relay somewhat diagrammatically since my invention may be readily applied to any type of relay of any general construction.

In general, the relay in Fig. 2 comprises a core 49 having two legs 53 and 54 upon which are respectively provided windings 6| and 62 that in closed-circuit, through an asymmetric unit 58, an armature 5| having a central-core 52 extending upwardly, a main alternating current winding 56 being mounted on said central-core, and a contact 51 actuated by the armature 5i.

As illustrated in Figs. 2 and 3, the core 49 comprises two inverted L-shaped members, hav-- ing their adjoining ends secured together in spaced relation by the side members 59 and 59', for the purpose of providing an opening 58 through which the central core 52 of the armature extends. The air gap that is provided hetween the central core 52 and the adjoining ends of the core 49, together with the side members 59 and 59' and through .which the alternating current flux set-up by the winding 56 must traverse, provides for limiting the maximum value-of said 5 flux. Moreover, by this construction, the chattering caused by a low-frequency alternating current is greatly alleviated, because the said'air-gap remains the same regardless of the position of the armature 5| and, in addition, the varying flux attraction at the said air gap caused by a lowfrequency flux is horizontal and does not have any chattering eifect upon the downward pull of the armature.

Two non-magnetic screws 64 and 65 are provided in threaded openings in the ends of the armature 5! for the purpose of providing an adjustable air gap. Accordingly, the drop-away value ofthe armature may be selected by adjusting the width of the said air gap. Also the non-magnetic screws prevent the armature from sticking to the core as a result of the residual magnetism established by the unidirectional flux.

For the purpose of convenience the flux path through the central-core 52 and the right-leg 53 will be designated as the right-hand magnetic circuit and the flux path through the central-core 52 and the left-leg 54 will be designated as the left-hand magnetic circuit.

The operation of the relay shown in Figs. 2 and 3 is slightly different from that shown in Fig. 1, since both of the legs 53 and 54 or the core are respectively provided with a winding connected in closed-circuit through an asymmetric unit 58. Assuming that the alternating current flux established by the winding 56 of the central core 52 is flowing upwardly and in the absence of the windings ti and 62 and the asymmetric unit 58, the flux would divide equally and circulate through the right and left hand magnetic circuits. 40 However, the action of the alternating-current flux is altered by means of the said windings and the asymmetric unit 58 and as a result a unidirectional flux indicated generally by the broken line 66 is established.

Assuming again that the alternating-current flux is flowing upwardly in the central core, and now as a result of the action of the said windings 6i and 62 and the asymmetric unit 58 that part of the flux which attempts to traverse the left-hand magnetic circuit is opposed by a flux set-up by the current which is induced in the winding 62, said current also flowing through the winding 6| and the asymmetric unit 58. On the other hand, the flux that traverses the righthand magnetic circuit is unopposed since the current that would be induced in the winding 6| is prevented from flowing through the asymmetric unit 58. In fact, it will be noted that the current induced in the winding 62, since it flows through the winding 6| establishes a flux in the leg 53 which flows in the same direction as that part of the alternating-current flux circulating through the right-hand magnetic circuit.

When the alternating-current flux of the central core reverses and flows downwardly, that part of said flux which tends to circulate in the right-hand magnetic circuit is opposed by the flux set-up by the current induced in the winding 6|. flux which traverses the left-hand magnetic circuit is unopposed. Moreover, the current induced in. the winding 6|, since it flows through the winding 62, establishes a flux in the left-leg On the other hand, that part of the 70 of the altemating-current flux circulating in the left-hand magnetic circuit. The resultant action of the flux is such as to establish a unidirectional flux,'indicated by the broken line 66, which circulates through the main core 49 and the armature 5|.

From the foregoing, it will be readily understood that the presence of the unidirectional flux provides for continuously attracting the armature 5! to the main core 49, while the flux produced by the winding 56 is passing through zero; even though the frequency of the alternatingcurrent flux approaches a relatively low value, such as it will in the control circuit illustrated in Figs. 5 and 6.

In this embodiment of the relay, since there is no by-pass for the alternating-current flux, such as the air gap l6 provided in the relay in Fig. 1, it is necessary to limit the current that flows through the winding 56 by operating the relay in series with some other electrical apparatus. That is to say, if the winding 56 were designed to operate across a source of constant potential, the impedance thereof would gradually decrease to a very low value since the main core 49 would eventually become completely saturated by the unidirectional flux. The alternating current flowing through the winding 56 would, consequently, increase inversely as the impedance thereof decreases, until it would reach a destructive value. However, when the winding 56 of the relay is operated in series with other electrical apparatus which limits the current to a value which the relay winding 56 can safely carry, even a large decrease in the impedance of the winding 56 is harmless because the value of the current is held substantially the same by the unchanged impedance of the windings of the external electrical apparatus.

At this point, it will be noted that the relay shown in Fig. 1 finds application in shunt or series circuits while the relay, shown in Figs. 2 and 3 finds application only in series circuits.

Referring to Fig. 5, which illustrates a control circuit utilizing a plurality of relays 226, 227 and 228 constructed substantially in accordance with the relay, shown in Figs. 2 and 3, except that they are respectively associated with a pilot relay and a mechanical interlock, which prevent the contacts of the said relays from operating unless the pilot relay and the mechanical interlock have previously operated.

The control circuit in Fig. 5, comprises generally a motor 226 having a primary winding 22l and a secondary winding 222, a plurality of sets of accelerating resistors 223, 224 and 225, adrum controller 236 having contact fingers 231 to 24l, inclusive and a plurality of pilot relays 232 to 235, inclusive, each associated with a mechanical interlock for electrically and mechanically controlling the operation of the relays 226, 221 and 228.

The mechanical interlocks are the same, and it is thought that a description of one of the said relays and its associated mechanical interlocks will be suificient. As illustrated, the mechanical interlock for the relay 226 comprises a hook-shaped release rod 255 having its lower end engaging the contact 25l from underneath, a spring 256 for biasing the release rod 255 upwardly, and a pivotally mounted arm 254 mechanically actuated by the armature of the pilot relay 232, and having its free-end disposed to depress the release rod 255 downwardly, against the action of the spring 256, when the pilot relay 232 is energized.

In this manner, the armature oi. the relay 226 is prevented from dropping, by means of gravity, unless the pilot relay 232 has been previously energized.

The winding N5 of the relay 226 is connected in series with one of the phases of the secondary windings of the motor 220 by the conductors 266 and 261. When the pilot relay 235 is-energized, the winding 2|! oi the relay 228 is connected in series with the same phase of the secondary winding of the motor 220, but at a point between the sets of resistors 224 and 225. Also, as illustrated, the closing of relay 235 excludes the set of re sistors 225 and the winding 2l5 of the relay 226 from the secondary circuit of the motor. Similarly, when the pilot relay 234 is energized the winding MB of the relay 221 is connected in series with the same phase of a secondary winding of a motor 220, but at a point between the sets of resistors 223 and 224. Likewise, the closing of the pilot relay 234 excludes the sets of resistors 224 and 225, and the windings of the relays 226 and 228 from secondary winding of the motor 220. Finally when the pilot relay 233 operates, all of the sets of resistors 223, 224 and 225 and the windings of all the relays 226, 228 and 227 are excluded from the secondary winding of the motor 220.

In the starting and in the accelerating of the motor 220, the drum controller 236, as is usual practice, may be immediately actuated to the full-on position, namely, position 1;. However, in case speed control of the motor is desired, the controller 236 may be advanced to any one of the positions to accommodate the operating conditions. At this time, I wish to point out that if speed control of the motor is not necessary, the drum controller 236 could be replaced by a starting push-button which would give the desired operations for starting and accelerating the motor 220.

When the drum controller 236 is immediately actuated to the full-on position, 0", for starting the motor 220, the pilot relay 232 immediately closes the main-line switch 242, which energizes the motor 220 from the three-phase supply conductors represented by the reference characters 229, 230 and 23L pilot relay 232 extends from the line conductor 23l, through conductor 263, contact fingers 231 and 23B, bridged by the drum controller 236, conductor 264, the winding of the pilot relay 232, and conductor 265, to the line conductor 23!].

As the armature of the pilot relay 232 moves upwardly, the pivotally mounted arm 254 depresses the hook release rod 256 and, in consequence frees thearmature of the relay 226 from the mechanical interlock. However, simultaneously with the depressing of the release rod 256, a voltage is induced in the secondary winding of the motor 220 which immediately energizes the winding 2| 5 of the relay 226 and, thereby, prevents the armature from falling and closing the contact 25l.

During the initial portion of the starting period of the motor 220, since the speed of the rotor is very low, the frequency of the current induced in the secondary winding 222 is approximately the same as the frequency of the primary circuit. However, as the speed of the rotor increases the frequency and current in the secondary winding decreases to such an extent that the attractive force of the flux produced by the winding 2I5 of The circuit for energizing the -ing the pilot relay 234.

the relay 226 becomes less than the force of gravity. When this flux condition occurs, the armature drops and closes the contact 251.

The closirm of the contact 25| establishes a circuit for energizing the pilot relay 235 which actuates the associated mechanical interlock to permit the relay 228 to be free to open. This circuit may be traced from the energized drum controller 238, through the contact finger 236, conductor 268, contact 25l, conductor 269, the winding of the pilot relay 235, and conductors 216 and 211 to the line conductor 230.

Operation of the pilot relay 235, in addition to operating the mechanical interlock, connects the winding 2|1 of the relay 228 in series with the same phase of the secondary winding of the motor 220, as the winding of the relay 226 was connected, but at a point between the sets of resistors 224 and 225. The circuit for connecting the winding 2 i 1 of the relay 228 in series with one phase of the secondary winding of the motor extends through conductor 214, the lower contacts of the pilot relay 235, conductor 215, the winding 2" of the relay 228, conductor 213 to the opposite side of the phase. Furthermore, the operation of the relay 235 excludes the relay 226 and the set of resistors 225 from the secondary winding of the motor 220 by, means of the shunting conductors 212, 213 and 214. Since the relay 228 is energized simultaneously with the operation of the mechanical interlock, the armature is prevented from dropping and closing the contact 253.

Just as soon as the set ofresistors 225 and the relay 226 are excluded from the secondary winding of the motor 220, the current induced therein suddenly increases from the previously low value to a higher value suflicient to operate the relay 228. However, as the motor gains speed the current and the frequency of the secondary winding gradually decreases to such an extent that the attractive force of the flux produced by the winding 2" of the relay 228 becomes less than the force of gravity, and the armature, accordingly, drops and closes the contact 253. The closing of the contact 253 establishes a circuit for energiz- This circuit may be traced from the energized drum controller 236 through the contact finger 248, conductor 260, contact 253, conductor 216, the winding of the pilot relay 234, and conductors 211 and 211 to the line conductor 238.

The pilot relay 234, when energized, actuates the mechanical interlock to free the armature of the relay 221, but at the same time it electrically connects the winding 2l6 of the relay 221 in series with the same phases of the secondary winding of the motor as the relays 226 and 228 were connected, but at a point between the sets of resistors 223 and 224. Since the relay 221 is simultaneously energized with the operation of the mechanical interlock, the armature is prevented from dropping and thereby closing the contact 252.

The circuit for connecting the main winding of the relay 221 in one phase of the secondary winding of the motor extends through conductor 280, the lower contacts of the pilot relay 234, conductor 28l, the main winding of the relay 221 and conductor 219, to the other side of the phase. The closing of the pilot relay 234, also excludes the sets of resistors 224 and 225, and the windings of the relays 226 and 228 from the secondary circuit of the motor by means of the shunting conductors 218, 219 and 280.

Just as soon as the sets of resistors 224 and 225, and the windings of the relays 226 and 228 are excluded, the current in the secondary winding suddenly increases from its previously low value to a higher value suiiicient to operate the relay 221. However, as the motor gains speed the current and the frequency of the secondary winding gradually reduces to such an extent that the attractive force of the flux produced by the winding 216 of the relay 221 becomes less than the force oi gravity, and its armature, accordingly, drops and-closes the contact 252.

The closing of the contact 252 establishes a. circuit for energizing the pilot relay 233 which, when operated, excludes all of the sets of resistors and the windings of the relays 226, 221 and 228 from the secondary circuit of the motor by means of shunting conductors 285, 286 and 281. Under this condition the motor runs at maximum speed. The circuit for energizing the pilot relay 233 extends from the energized drum controller 236 through the contact finger 241, conductor 282, contact 252, conductor 283, the winding of the pilot relay 233 and conductors 284 and 211 to the line conductor 238.

In this connection, it will be noted that, as the speed of the rotor increases, the frequency of the current induced in the secondary winding of the motor approaches a very low value which offers an opportunity for the armature of the relays 226, 228 and 221, particularly relay 221 to chatter or even drop while the induced current passes through zero. However, the unidirectional flux produced by the illustrated windings and their respective asymmetric units, provide for continuously attracting the armature while the low frequency flux passes through zero.

From the foregoing description of the operation, it has been observed that by immediately actuating the drum controller 236 to the full on position, the motor is automatically accelerated by the operation of the relays226, 228 and 221.

However, if it is desirable to operate the motor less than maximum speed, this may be done by actuating the drum controller on one of the less advanced positions. Minimum speed may be attained by actuating the drum controller 236 on position s. In this position all of the sets of resistors 223, 224 and 225 are included in the secondary winding of the motor, since the circuits for energizing the said pilot relays are interruptedat the contact fingers of the drum controller 236, except that for the pilot relay 232. By advancing the drum controller 236 to position it, the circuit is established for energizing the pilot relay 235 which, accordingly, excludes the set of resistors 225 from the secondary winding of the motor and thereby effects a slightly higher speed. A still higher speed may be attained by actuating the drum controller 236 to positions u, and finally maximum speed is attained when the controller is actuated to position 0".

In this particular control system since the frequency of the secondary winding of the motor 22!) decreases to a very low value as the motor approaches synchronous speed, relays of the type shown in Figs. 2 and 3 find very useful application, because the unidirectional flux pro- P vides for continuously attracting the armature while the low frequency alternating current flux is passing through zero.

The relay of the type shown in Figs. 2 and 3, also finds very useful application in the control circuit shown in Fig. 6.

Generally, the control circuit in Fig. 6 comprises a synchronous motor 300, a starting transformer having windings 342 and 343, dual Operated starting relays 332 and 333 mechanically interlocked by a pivotally mounted member 347, a relay 304 of the type shown in Figs. 2 and 3, a time element relay 326 of the dash-pot type, and a line relay 399.

The synchronous motor 300 is of the conventional type having an alternating-current primary winding 302 and a direct-current winding 30l. The starting transformer having windings 342 and 343 is energized from a polyphase alternating-current source represented by the line conductors 329, 330 and 33!. The windings 342 and 343 of the transformer are so interconnected with the primary winding 302 of the synchronous motor 300 that substantially one-half of the line potential is impressed upon the said winding when the contacts of the relay 332 are closed and that the full line potential is impressed upon the said winding when the contacts of the relay 333 are closed. This arrangement is in accordance with the usual method of starting synchronous motors, in that, substantially one-half of the line potential is impressed upon the primary winding during the initial portion of the starting period, and then, after the motor attains a predetermined speed, the full line potential impressed upon the said winding.

The time sequence operation of the dual starting relays 332 and 333 is accomplished by the time element relay 326 of the dash-pot type. When the lower contacts of the relay 326 are closed a circuit is established for energizing the starting relay 332, which when operated, closes its own contacts and which opens those of the relay 333 by means of the interlock 34?. After a predetermined length of time depending upon the delayed action of the dash-pot, the relay-826 closes its upper contacts and establishes a circuit for energizing the starting relay 333 which, when operated, closes its own contacts and which opens those of the relay 332 by means of the interlock 341.

The relay 304 is of the type shown in Figs. 2 and 3 and, when the line relay 309 is closed during the starting period, said relay is connected in series circuit relation with the direct current winding 30l of the motor 300 which is closed upon itself, through a circuit extending from one terminal of the motor field winding 30l, conductors 312 and 3I3, the relay winding 305, conductor 314, lower contacts of the relay 309, conductors 365 and 3l0 to the opposite terminal of the motor field winding 30l. As a result the relay 304 is energized by the current induced in the winding 30l. In this connection, when the speed of the motor is low as it will be during the initial portion of the starting period, the frequency of the current induced in the winding 3M is substantially the same as the frequency of the alternating current supply source. -However, as the speed of the motor approaches synchronous speed, the frequency thereof becomes less and less until finally the relay 304 drops to establish a circuit for energizing the line relay 309 which connects the direct current supply conductors 391 and 308 to the direct current winding 30H, through conductors 340 and 32 i.

In p a ing the operation of the control cir cuit, I will assume that the alternating current supply conductors 329, 330 and 33l are energized, together with the direct current supply com tors 301 and 308, and that the manually operated switch 328 has just been closed. The closing of the switch 328 establishes a circuit for energizing the time delay relay 326 and the starting relay 332. The circuit for energizing the time element relay 326 may be traced from the supply conductor 330 through conductor 35l, the switch 328, conductors 352 and 353, the winding of the relay 326, and conductors 354 and 355. to the supply conductor 329. The parallel circuit for energizing the relay 332 may be traced from the energized conductor 352, through conductor 356, the lower contacts of the relay 326, conductor 351, and the winding of the relay 332 to the supply conductor 329.

Operation of the relay 332 connects one-half of the windings 342 and 343 to the primary winding 302 of the synchronous motor. The line conductor 329 is connected to the terminal 3| 6 of the winding 302 through a conductor 358, the contacts 331, the upper half of the winding 342, the contacts 338 and the conductor 359; the supply conductor 330 is connected to the terminal 3" of the primary winding through a conductor 362, the contacts 339, and conductors 36l and 360, and the supply conductor 33| is connected to the terminal 3l8 of the primary winding through a conductor 363, the contacts 3, the lower half of the winding 343, the contacts 340 and the conductor 364.

Therefore, one-half of the line potential is impressed upon the primary winding of the synchronous motor when the contacts of the relay 332 are closed. As will be observed, this condition only exists for a brief period of time, depending upon the time delay action of the relay 326 afforded by the dash-pot 321. In practice, the delayed action of the relay 326 is of such duration that the motor attains a speed of such value that the back induced voltage thereof is great enough to oppose the full line potential without causing injury to the motor windings.

When the relay 326 operates and closes its upper contacts a circuit is established for energizing the starting relay 333, and at the same time, the circuit for energizing the relay 332 is interrupted. The circuit for energizing the relay 333 extends from the energized conductor 352 through the upper contacts of the relay 326, conductor 344, the winding of the relay 333, and conductors 345, 346 and 355 to the supply conductor 329. The closing of the contacts of the relay 333 impresses the full line potential upon the primary winding of the synchronous motor, bringing it up to full speed. As will be observed, the supply conductors 329, 330 and 33l are, respectively, connected to the terminals 3| 6, 3H and 3I8 of the primary winding of the synchronous motor by means of the contacts 334, 335 and 339.

As is usual practice, in starting synchronous motors, the direct current winding is short-circuited and, accordingly, the synchronous motor is operated as a straight induction motor until it obtains substantially full speed, and then the direct-current winding is open-circuited and energized from a source of direct current. As shown, during the starting period, the directcurrent winding 30i is short-circuitcd through the lower contacts of the relay 309, under this condition the winding 305 of the relay 304 is connected in series-circuit relation with the shortcircuited winding 30!.

During the initial portion of the starting period the frequency and the magnitude of the current induced in the short-circuited winding is suflicient to operate the relay 304, thus opening the contacts 306. However, as the speed of the motor increases the frequency of and the current induced in, the secondary circuit 30! gradually becomes less and less until the armature of the relay 394 drops and closes the contacts 306.

When the armature of the relay 304 closes the contacts 393 a circuit is established for energizing the line switch 309 for delivering direct current to the winding 3lll of the synchronous motor. The circuit that energizes the relay 3539 may be traced from the energized conductor 352 through the upper contacts of the relay 326, conductor 3| 9, the winding of the relay 309, conductor 320, contacts 366, and conductors 32l, 346 and 355 to the supply conductor 329.

Inasmuch as the frequency and the current of the secondary circuit 30l becomes less and less as the motor speeds up, I find that relays of the general type, even though having a shading coil, chatter and vibrate a great deal. This is particularly true, just prior to the drop-away of the armature. On the other hand, the relay 304, since it establishes a uni-directional flux throughout the core and its armature, provides for reducing substantially all of the chattering generally incident in other types of relays. Herein resides the utility of my directional flux relay.

I find that it is of prime importance to prevent the relay 384 from chattering. The preventing of chattering materially increases the useful life of the relay.

Since certain changes in my invention may be made without departing from the spirit and scope thereof, it is intended that all matters contained in the foregoing description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. In combination, a magnetic circuit, means for establishing a reversing flux in said magnetic circuit, and means influenced by said reversing flux for establishing a unidirectional flux in said magnetic circuit.

2. In combination, a magnetic circuit, means for establishing a reversing flux in said magnetic circuit, and a winding influenced by said reversing flux, a rectifier in circuit with said winding, said winding and rectifier thus offering a relatively high resistance to the fiow of the induced current caused by the said reversing flux in one direction and a relatively low resistance to the flow of said current in the opposite direction to produce a unidirectional flux in said magnetic circuit.

3. In combination, a structure having a plurality of magnetic circuits, a main winding for establishing a reversing flux. in said magnetic circuits, a second winding influenced by said reversing flux, and an asymmetric unit in series with said second winding for permitting current to flow in one direction but not in the other direction to produce a unidirectional flux in one of said magnetic circuits.

4. In combination, a magnetic circuit, a main winding for establishing a reversing flux in said magnetic circuit, a second winding influenced by said reversing flux, an asymmetric unit in series with said second winding for permitting current to flow in one direction but not in the other direction, and a third winding disposed to dissipate the residual flux when the main winding is deenergized.

5. In combination, a core having a multiple of magnetic circuits, means for establishing a reversing flux in said circuits, and a winding including an asymmetric unit influenced by the reversing flux that is traversing one of the said magnetic circuits, said winding and asymmetric unit thus offering a higher resistance to the flow of current in one direction than in the other direction.

6. In combination, a magnetic circuit, a winding including an asymmetric unit ofiering a higher resistance to the flow of current in one direction than in the other direction associated with said magnetic circuit, asecond magnetic circuit associated with said first-mentioned magnetic circuit, said second magnetic circuit having a higher reluctance than said first-mentioned magnetic circuit, and means for establishing a reversing flux in both of. said magnetic circuits.

7. In combination, a magnetic circuit, means for establishing a reversing flux in said magnetic circuit, means influenced by said reversing flux for establishing a unidirectional flux in said magnetic circuit, and a second magnetic circuit associated with said first-mentioned magnetic circuit for limiting said unidirectional flux.

8. In a relay, in combination, a core having an armature disposed in alignment therewith, a main winding for establishing a reversing flux in said core, and a second winding influenced by said reversing flux for establishing a unidirectional flux in said core and armature, and means associated with said second winding for permitting current to flow in one direction but not in the other direction.

9. In a relay, in combination, a magnetic circuit, a winding for said magnetic circuit, means for energizing said winding with alternating current, means influenced by said alternating current for establishing a unidirectional flux in said magnetic circuit, and means for dissipating said flux in said magnetic circuit, means influenced by said reversing flux for establishing a unidireccircuit having a greater reluctance than the flrstmentioned magnetic circuit.

11. In a control system, in combination, a relay having an armature energized by a source of alternating current of relatively low frequency, and means associated with the relay for producing a unidirectional flux for"'c0ntinuously holding the armature closed as the low-frequency current passes through zero.

12. In a control system, in combination, a relay having an armature, energized by a source of alternating current, and a core member, and means comprising only a coil and an asymmetric unit in closed circuit relation disposed on the core mem-- her and adapted to continuously hold the armature closed as the alternating current passes 

